Add HydePHP 2 migration plan and wire it into docs navigation

[Copilot]

This issue asks for a concrete plan to migrate the site from Jekyll to HydePHP 2. This PR adds an implementation-grade migration blueprint and makes it discoverable from both docs navigation and repository onboarding docs.

• Migration blueprint (docs/guides/hydephp-migration-plan.md)

  • Defines phased cutover: Hyde bootstrap, template/data port, markdown content migration, asset pipeline parity, and CI/deploy transition.
  • Captures route/content preservation requirements, validation checkpoints, and risk controls for incremental delivery.

• Docs navigation update (_data/menu.yml)

  • Adds a new Guides entry for direct access to the migration plan in-site.

• Repository entrypoint update (README.md)

  • Adds a Migration Planning section linking to the new plan so contributors land on the strategy immediately.

Guides:
  Getting started: '/docs/guides/getting-started'
  Creating middleware: '/docs/guides/creating-middleware'
  HydePHP migration plan: '/docs/guides/hydephp-migration-plan'

• Fixes Migrate from Jekyll to HydePHP #60

[DannyvdSluijs]

@copilot the plan should be used input for the agent not as public documentation. Can you update the pr description with the plan and execute the plan?

[Copilot]

@copilot the plan should be used input for the agent not as public documentation. Can you update the pr description with the plan and execute the plan?

Done in 51d80cf. I removed the public migration-plan doc/nav references, put the execution plan directly in the PR checklist, and executed the migration to HydePHP 2 (project bootstrap, content and asset migration, and Jekyll file removal).